The Salmonella strains TA-100 and TA-1535 have been used to test for the mutagenicity of Tris-BP, a known carcinogen, and some of its metabolites. The chemical structures of a series of metabolites were determined and the metabolites were synthesized at NIEHS. A gradient of mutagenic responses was seen when the metabolites were tested. These responses ranged from very weakly positive to as mutagenic as the parent compound. All positive responses required Aroclor-induced rat liver S-9. Testing trimethylphosphate (a direct-acting mutagen) and tripropylphosphate (a non-mutagen) supported the fact that the leaving group, 2-3 dibrompropyl phosphate, is responsible for TRIS-BP mutagenicity with the metabolite, 2-bromopropene, contributing some additional mutagenicity. Both compounds are direct-acting mutagens.